The energy for operating a power supply grid is supplied by various and different types of power stations. Herein, most of the power stations, such as nuclear power stations, coal-fired power stations, gas-fired power stations, wind turbines, biogas plants, or solar power plants, are nothing but energy generators for feeding energy into the non-local power supply grid. For example, non-local power supply grids are distribution networks and transmission networks, such as they are operated in Germany by Amprion, 50 Hertz, Tennet, and TransnetEnBW. These transmission networks are a part of the wide area synchronous grid in Europe. In their capacity as mere energy generators, the power stations mentioned above cannot take up any extra energy from the grid and store it in case of need. In contrast, energy storage systems can be used to absorb energy from and release it to a power supply grid. For example, energy storage systems are central energy storage systems, such as pumped storage power stations, or decentralized energy storage systems, such as battery storage devices or flywheel energy storage units. Pumped storage power stations are energy storage systems that are largely not subject to changes in weather and, as a general rule, are therefore always available. Usually, central energy storage systems are designed for a large capacity. Due to the available capacity, such systems are adapted to provide reserve energy for the non-local power supply grid in order to take appropriate effect in the non-local power supply grid. Depending on their overall size, pumped storage power stations may have a capacity of several 100 MW and more wherein, however, the generators are, in most cases, designed to produce electric current under full load and can therefore utilize the full capacity of the pumped storage power station at an appropriate efficiency and in a timely manner. This operating method is not adapted to stabilize or improve the quality of a small local power supply systems having a demand for electricity that is rather negligible as compared with the capacity of the pumped storage power station.
Centrally used battery storage devices are currently under construction with the objective to put into practice a pilot operating method for grid-stabilizing (non-localized) tasks (reserve energy). However, the devices that have been planned so far do not fulfill any localized tasks. Due to their immanent relationships between output, capacity and aging, however, battery storage devices are, as a matter of principle, not very well suited for such applications with a plurality of load cycles per day and degrade rapidly because of temperature influences, system failures and operating errors. For this reason, battery storage devices require highly intensive maintenance. Due to their high fire and chemical risks, battery storage devices additionally present an environmental and/or water hazard and are highly complex in terms of protection and security.
In general, decentralized energy storage systems are optimized for stabilizing the local demand for electricity and are neither designed nor qualified for delivering reserve energy to support the non-local power supply grid. Such systems cannot contribute to fulfilling the demands of all power supply grids. An interconnection of the decentralized storage systems to form a system that is operated both locally and non-locally has not been achieved so far.
For this reason, it would be desirable to have an effective energy storage system available which allows achieving an improvement in the quality of local grids and, at the same time, the security of energy supplies for non-local power supply grids as required and can therefore be operated as an energy storage system having an adequate effect for both purposes.